Re: [PATCH v3 02/13] mm/huge: avoid big else branch in zap_huge_pmd()

Suren Baghdasaryan
2026-03-28T18:52:48Z

On Fri, Mar 20, 2026 at 11:07 AM Lorenzo Stoakes (Oracle)
<ljs@kernel.org> wrote:
>
> We don't need to have an extra level of indentation, we can simply exit
> early in the first two branches.
>
> No functional change intended.
>
> Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> Acked-by: Qi Zheng <zhengqi.arch@bytedance.com>
> Signed-off-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>

Reviewed-by: Suren Baghdasaryan <surenb@google.com>

> ---
> mm/huge_memory.c | 87 +++++++++++++++++++++++++-----------------------
> 1 file changed, 45 insertions(+), 42 deletions(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 2775309b317a..4e8df3a35cab 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -2328,8 +2328,10 @@ static inline void zap_deposited_table(struct mm_struct *mm, pmd_t *pmd)
> int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
> pmd_t *pmd, unsigned long addr)
> {
> - pmd_t orig_pmd;
> + struct folio *folio = NULL;
> + int flush_needed = 1;
> spinlock_t *ptl;
> + pmd_t orig_pmd;
>
> tlb_change_page_size(tlb, HPAGE_PMD_SIZE);
>
> @@ -2350,59 +2352,60 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
> if (arch_needs_pgtable_deposit())
> zap_deposited_table(tlb->mm, pmd);
> spin_unlock(ptl);
> - } else if (is_huge_zero_pmd(orig_pmd)) {
> + return 1;
> + }
> + if (is_huge_zero_pmd(orig_pmd)) {
> if (!vma_is_dax(vma) || arch_needs_pgtable_deposit())
> zap_deposited_table(tlb->mm, pmd);
> spin_unlock(ptl);
> - } else {
> - struct folio *folio = NULL;
> - int flush_needed = 1;
> + return 1;
> + }
>
> - if (pmd_present(orig_pmd)) {
> - struct page *page = pmd_page(orig_pmd);
> + if (pmd_present(orig_pmd)) {
> + struct page *page = pmd_page(orig_pmd);
>
> - folio = page_folio(page);
> - folio_remove_rmap_pmd(folio, page, vma);
> - WARN_ON_ONCE(folio_mapcount(folio) < 0);
> - VM_BUG_ON_PAGE(!PageHead(page), page);
> - } else if (pmd_is_valid_softleaf(orig_pmd)) {
> - const softleaf_t entry = softleaf_from_pmd(orig_pmd);
> + folio = page_folio(page);
> + folio_remove_rmap_pmd(folio, page, vma);
> + WARN_ON_ONCE(folio_mapcount(folio) < 0);
> + VM_BUG_ON_PAGE(!PageHead(page), page);
> + } else if (pmd_is_valid_softleaf(orig_pmd)) {
> + const softleaf_t entry = softleaf_from_pmd(orig_pmd);
>
> - folio = softleaf_to_folio(entry);
> - flush_needed = 0;
> + folio = softleaf_to_folio(entry);
> + flush_needed = 0;
>
> - if (!thp_migration_supported())
> - WARN_ONCE(1, "Non present huge pmd without pmd migration enabled!");
> - }
> + if (!thp_migration_supported())
> + WARN_ONCE(1, "Non present huge pmd without pmd migration enabled!");
> + }
>
> - if (folio_test_anon(folio)) {
> + if (folio_test_anon(folio)) {
> + zap_deposited_table(tlb->mm, pmd);
> + add_mm_counter(tlb->mm, MM_ANONPAGES, -HPAGE_PMD_NR);
> + } else {
> + if (arch_needs_pgtable_deposit())
> zap_deposited_table(tlb->mm, pmd);
> - add_mm_counter(tlb->mm, MM_ANONPAGES, -HPAGE_PMD_NR);
> - } else {
> - if (arch_needs_pgtable_deposit())
> - zap_deposited_table(tlb->mm, pmd);
> - add_mm_counter(tlb->mm, mm_counter_file(folio),
> - -HPAGE_PMD_NR);
> -
> - /*
> - * Use flush_needed to indicate whether the PMD entry
> - * is present, instead of checking pmd_present() again.
> - */
> - if (flush_needed && pmd_young(orig_pmd) &&
> - likely(vma_has_recency(vma)))
> - folio_mark_accessed(folio);
> - }
> + add_mm_counter(tlb->mm, mm_counter_file(folio),
> + -HPAGE_PMD_NR);
>
> - if (folio_is_device_private(folio)) {
> - folio_remove_rmap_pmd(folio, &folio->page, vma);
> - WARN_ON_ONCE(folio_mapcount(folio) < 0);
> - folio_put(folio);
> - }
> + /*
> + * Use flush_needed to indicate whether the PMD entry
> + * is present, instead of checking pmd_present() again.
> + */
> + if (flush_needed && pmd_young(orig_pmd) &&
> + likely(vma_has_recency(vma)))
> + folio_mark_accessed(folio);
> + }
>
> - spin_unlock(ptl);
> - if (flush_needed)
> - tlb_remove_page_size(tlb, &folio->page, HPAGE_PMD_SIZE);
> + if (folio_is_device_private(folio)) {
> + folio_remove_rmap_pmd(folio, &folio->page, vma);
> + WARN_ON_ONCE(folio_mapcount(folio) < 0);
> + folio_put(folio);
> }
> +
> + spin_unlock(ptl);
> + if (flush_needed)
> + tlb_remove_page_size(tlb, &folio->page, HPAGE_PMD_SIZE);
> +
> return 1;
> }
>
> --
> 2.53.0
>